1. Field of the Invention
The invention relates to fertilizer compositions comprising an aqueous composition including ammonium thiosulfate; and a complex of a metal ion and a chelating agent, wherein the complex lowers the freeze point of the aqueous composition when creating a liquid fertilizer including the ammonium thiosulfate and the complex. Optionally, the liquid fertilizer includes borate ions. Methods of using the liquid fertilizer are also disclosed.
2. Description of the Related Art
Various elements, which are normally drawn from the soil, are known to be essential to plant nutrition. These elements include: nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), boron (B), molybdenum (Mo), and chlorine (Cl). Of these elements, nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium are needed by plants in relatively large quantities and are therefore called macronutrients. The remaining members of the group (iron, manganese, copper, zinc, boron, molybdenum, and chlorine) are known as micronutrients since they are required in very small amounts for plant growth.
Ammonium thiosulfate (ATS, 12-0-0-26, N-P-K-S) is emerging as a key nutrient product for corn cultivation. Along with providing both high levels of elemental nitrogen and sulfur in an easy and safe to handle aqueous liquid form, ATS also provides some level of urease inhibition. Another key property of ATS is that when combined with a urea-ammonium nitrate (UAN) solution at a 1:10 ratio, ATS lowers the freeze point (salt out temperature) of UAN from roughly 32° F. to 0° F. Lowering the salt out temperature has a tremendous advantage for storing the product over cold winter months as dealers/suppliers can eliminate or reduce costly heating systems and storage equipment. ATS can be added to a UAN solution in solid form or as an aqueous solution.
While aqueous solutions of ammonium thiosulfate are beneficial as a liquid fertilizer and as a liquid freezing point depressant for UAN solutions, aqueous solutions of ammonium thiosulfate do have certain disadvantages. One major disadvantage of aqueous solutions of ammonium thiosulfate is that they are temperature sensitive in that they begin to crystallize out of solution as the solution temperature decreases. Crystallization causes problems such as plugging of lines, applicator nozzles, storage tanks, etc., as well as reducing the nutrient value of a fertilizer that includes the aqueous ammonium thiosulfate. Consequently, liquid fertilizers have been limited to use and storage where the ambient temperature is above the crystallization temperature of the liquid fertilizer.
Thus, there is a need for stable liquid fertilizer compositions that include ammonium thiosulfate (which provides advantageous levels of the macronutrients nitrogen and sulfur) and plant nutrients (such as other macronutrients and/or micronutrients), and that will not crystallize during cold temperatures, particularly sub-zero temperatures.